Froment sign is a special test of the hand for weakness of the ulnar nerve, specifically, the action of adductor pollicis.
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Process of examination
A patient is asked to pinch an object, usually a flat object such as a piece of paper, between the thumb and index finger (pinch grip). The examiner then attempts to pull the object out of the subject's hand.
- A person with notable weakness of the adductor pollicis due to advanced ulnar neuropathy will flex the thumb using the flexor pollicis longus.
- Froment sign is the flexion of the interphalangeal joint of the thumb rather than adduction of the entire thumb.
- The flexor pollicis longus is nearly always innervated by the anterior interosseous branch of the median nerve.
- Simultaneous hyperextension of the thumb MCP joint is indicative of ulnar nerve compromise. This is also known as Jeanne's sign.